A chromogenic azobenzene compound, (E)-(3,3'-(diazene-1,2-diyl)bis(3,1-phenylene))bis(diphenylmethanol), forms lattice inclusion compounds with a range of common solvents. It is yellow in the unsolvated crystalline form, but orange or orange-red when crystallized as solvates with guest molecules that contain hydrogen-bond acceptors. Close examination of crystal structures of unsolvated and solvated forms reveals that differences in hydrogen bonding and a change in conformation of the azobenzene core are responsible for the change in lambda of absorption of the chromophore and hence color of the crystals. Hirshfeld surfaces and fingerprint plots reveal subtle differences in intermolecular interactions in the solvated and unsolvated crystalline forms.
Scott, Janet L. Almesaker, Ann Sumi, Yoshinori Tanaka, Koichi